12/1/10
The Problem with Recipes and High Tech Gadgets
I recently returned from a two week Introduction to Bladesmithing class at Haywood Community College in Clyde, NC. The instructors were Jason Knight and Burt Foster. The class was fantastic. It was amazing to have so much access to two very talented ABS masters. I came home with a brand new plan and some new recipes…well, for heat treatment at least.
I ordered low temp “Nitreblue” salts from Brownell’s, welded up a 304 stainless pipe to serve as a low temp salt tank for tempering, and built a heat treat forge we call “the sow’s belly”. I also ordered a hot plate to power the low temp salt tank, as well as two thermocouples and two PID controllers to use as pyrometers.
Well, I got it all together and figured I was in the modern age now with my heat treating – no more judging temps by eye and a magnet; no more toaster oven for tempering. I had acquired some new recipes, some new equipment and was ready to put them to use. It all seemed to work great until the trouble began. My blades were coming out softer than they should have and, when tested to destruction, my grain was not as fine as I thought it should be. Then the hot plate gave up after the third session.
Back to the drawing board.
I had introduced a whole new set of variables to my process - new recipes and new “cooking” equipment, but it wasn't working and I wasn't sure why. The pyrometers and thermocouples looked so high tech, were reading to a single degree, and seemed to be reading about right at room temperature, so I trusted them implicitly. I mean, they had to be much smarter than me or anything I had done in the past, right? Wrong.
After running into trouble, I started back tracking. Per a new recipe (not provided by Burt or Jason), I was running the heat treat forge right at 1500 deg F. That should be spot on for 1084, which I was using at the time. I was tempering two 2-hour cycles at 400 deg F, which Kevin Cashen recommends on his site, but as I said earlier, I was having problems. I started my investigation with the heat treat forge. Surprise, surprise I was reaching non-magnetic a little below 1425 deg F according to the pyrometer, so I tried quenching at 1450 instead of 1500. The scale blew off (a good sign) and, after grinding below the decarb, a file would not cut the blade. Off to the vise and snap…wow the grain was much finer now.
Next, I tackled the low temp salts. I am still having a bear of a time regulating them, but anyway, upon checking them with a turkey frying thermometer, I found a thirty degree discrepancy. I lowered my tempering setting to 350-360 and got a blade that held a much better edge. I am still working with all of it, but finally feel like I am getting somewhere positive.
The moral of the story is…someone else’s recipe may not work in your shop and high tech gadgets don’t assure accuracy out of the box. The magnet will not lie on ascending temps and you have to judge tempering by the way it cuts, not by a thermometer. Final word – write your own recipe and all electronics should be tested and calibrated prior to giving them your trust.
